Interest in fuel cell batteries as power sources for portable electronic devices has grown. A fuel cell is an electrochemical cell that uses materials from outside the cell as the active materials for the positive and negative electrode. Because a fuel cell does not have to contain all of the active materials used to generate electricity, the fuel cell can be made with a small volume relative to the amount of electrical energy produced compared to other types of batteries.
Fuel cells can be categorized according to the types of materials used in the positive electrode (cathode) and negative electrode (anode) reactions. One category of fuel cell is a hydrogen fuel cell using hydrogen as the negative electrode active material and oxygen as the positive electrode active material. When such a fuel cell is discharged, hydrogen is oxidized at the negative electrode to produce hydrogen ions and electrons. The hydrogen ions pass through an electrically nonconductive, ion permeable separator and the electrons pass through an external circuit to the positive electrode, where oxygen is reduced.
In some types of hydrogen fuel cells, hydrogen is formed from a fuel supplied to the negative electrode side of the fuel cell. In other types of hydrogen fuel cells, hydrogen gas is supplied to the fuel cell from a source outside the fuel cell. A fuel cell system can include a fuel cell battery, including one or more fuel cells, and a hydrogen source, such as a hydrogen tank or a hydrogen generator. In some fuel cell systems, the hydrogen source can be replaced after the hydrogen is depleted. Replaceable hydrogen sources can be rechargeable or disposable.
A hydrogen generator uses one or more reactants containing hydrogen that can react to produce hydrogen gas. The reaction can be initiated in various ways, such as hydrolysis and thermolysis. For example, two reactants can produce hydrogen and byproducts when mixed together. A catalyst can be used to catalyze the reaction. When the reactants react, reaction products including hydrogen gas and byproducts are produced.
In order to minimize the volume of the hydrogen generator, volume that is initially occupied by the reactants can be used to accommodate reaction products as the reactants are consumed by arranging the components of the hydrogen generator in a volume exchanging configuration. As reactants are consumed, volume that they had occupied is simultaneously made available to contain reaction products.
The hydrogen gas is separated from byproducts and unreacted reactants, and the gas exits the hydrogen generator and is provided to the fuel cell battery. Various means for separating the hydrogen gas are known, including porous filters to separate solids from the hydrogen gas and gas permeable, liquid impermeable membranes to separate the hydrogen gas from liquids.
It is desirable to further improve the volume efficiency of hydrogen generators while providing for effective separation of the hydrogen gas from reaction products and unreacted reactants. It is also desirable to provide a hydrogen generator having a simple design that is easily manufactured at a low cost.